Major Bullet Dodged

[Strife]

Take a look at this thread:

Cam Sprocket Wear

If you read on, you will see that at 25K miles on a new timing chain and all other items, I broke a (replaced) chain guide!

I'm considering obtaining a METAL guide to replace it.

Does anyone have any opinion on this? Why did MB get away from metal?

[Roncallo]

Originally Posted by Strife

Take a look at this thread:

Cam Sprocket Wear

If you read on, you will see that at 25K miles on a new timing chain and all other items, I broke a (replaced) chain guide!

I'm considering obtaining a METAL guide to replace it.

Does anyone have any opinion on this? Why did MB get away from metal?

MB went to plastic because it is in incredibly cheep process compared to metal. I also prefer the bolt on metal cam oilier fittings used on the iron engines.

[mbboy]

Originally Posted by Roncallo

MB went to plastic because it is in incredibly cheep process compared to metal. I also prefer the bolt on metal cam oilier fittings used on the iron engines.

Sure. The plastic guides retail for about 3.00, and the metal ones for about 20.00. Multiply that by 5 per engine, then by the number of cars MB made after the switch, and you have a significant increase in MB profits. Unfortunately, customers paid had to pay for that with blown engines and the cost of replacing the guides every 100k miles

[Ara T.]

Originally Posted by mbboy

Sure. The plastic guides retail for about 3.00, and the metal ones for about 20.00. Multiply that by 5 per engine, then by the number of cars MB made after the switch, and you have a significant increase in MB profits. Unfortunately, customers paid had to pay for that with blown engines and the cost of replacing the guides every 100k miles

Couldn't MB have charged an extra 20 dollars to the MSRP of the car? Who would bat an eye at 20 dollars if the car cost 40-70K or whatever ungodly amount these cost when new?

[Alkraut]

I don't think that the MB engineers believed that the nylon guides would be a problem. Tough, high temp plastic is ideal for this application. They most likely did much durability testing and were convinced of it's worthiness. What they could not adequatley simulate were the effects of time, not mileage, on the nylon. It loses it's plasticity over time in some environments. Certainly the case here.

[Strife]

Originally Posted by Alkraut

I don't think that the MB engineers believed that the nylon guides would be a problem. Tough, high temp plastic is ideal for this application. They most likely did much durability testing and were convinced of it's worthiness. What they could not adequatley simulate were the effects of time, not mileage, on the nylon. It loses it's plasticity over time in some environments. Certainly the case here.

But unless these things had been sitting in a warehouse for a decade, I don't think that they are more than 2.5 years old.

My present guesses as to the premature failure are:

1. Failed tensioner (which is 2.5 years and 25K miles old).
2. An incident at 105K miles which burned up the RH cam and the cam bearings put high loads on the chain, stretching it, causing premature wear to the cam gears, and the slapping eventually broke the plastic, which would have otherwise been fine

Although I'm basically changing everything involving the timing chain including the cam gears, putting in metal guides will give me a little more insurance in the event that this happens again. I can change the gears on the top, but not the crank gear, and who knows what that looks like.

[mbboy]

Originally Posted by Strife

My present guesses as to the premature failure are:

1. Failed tensioner (which is 2.5 years and 25K miles old).

Strife,

What makes you think your tensioner -- a Febi I assume -- failed after only 25k miles? i've heard they're very reliable for at least 100k, but i guess it's possible.

[Strife]

I think it MIGHT be the tensioner because I was getting rattle on start-up, but maybe that was just because the chain/gears are bad. I don't know. I'm contemplating putting the old one back in and seeing how it goes, but I do have a new spare. There are people on this website who claim that any tensioner not made by MB is garbage. I can't say.

I did get in two metal guides, by Meyle, pictured here. They seem to be cast(?) aluminum, with a fairly hard rubber bound to the top, and the rubber beveled on each side. I would have thought it could be a machined part or an extrusion. The picture below shows a 560SL(M117) plastic part similar, but not exactly the same size. I do not know if the 380(M116)parts had round or egg-shaped holes for the pins, I'll find out soon. But I do recall that the new plastic guides moved a little bit when I installed them. The Meyle website claims that they won't break but you will get plenty of warning noise when everything else starts to wear.

I don't think there are similarly-constructed M117 parts. These are also claimed to fit the 350 and 420. They were about 8x more expensive, but I swear I'm not going to do this job again (at least not on THIS car...).